WL Results

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1

I’ve been running WL test…If I use all different Gantry/Col/Couch angles it gives following result below. I use 4 different Gantry angles as well as 4 for col and 4 for couch angles. results show lots of 0s for RMS gantry/Col/Couch angles.

What is the ideal set of parameters? or do I need keep 2 parameters at 0 then move the 3rd? IE G=0, Couch = 0, and COL=30,60,90,0?

“Number of images: 10
Maximum 2D CAX->BB distance: 0.92mm
Median 2D CAX->BB distance: 0.48mm
Shift to iso: facing gantry, move BB: RIGHT 0.14mm; OUT 0.22mm; DOWN 0.27mm
Gantry 3D isocenter diameter: 0.00mm (0/10 images considered)
Maximum Gantry RMS deviation (mm): 0.00mm
Maximum EPID RMS deviation (mm): 0.00mm
Gantry+Collimator 3D isocenter diameter: 0.90mm (4/10 images considered)
Collimator 2D isocenter diameter: 0.00mm (1/10 images considered)
Maximum Collimator RMS deviation (mm): 0.00
Couch 2D isocenter diameter: 0.00mm (0/10 images considered)
Maximum Couch RMS deviation (mm): 0.00”

2

Hi Stephen,

I do not know if there is an ideal set of parameters (never read papers on the topic). At our clinic we use the following angles:
wl.PNG

there is a paper for a multi target winston lutz: https://iopscience.iop.org/article/10.1088/2057-1976/ac8e72
They use the following settings:
mtwl.png

regards,
Thomas

3

Pylinac uses all-else-must-be-0 logic for the axis-specific evaluations. E.g. for the gantry 3d isocenter diameter couch and collimator must be 0. This does not affect the max/median CAX->BB distances or the shift to iso. So the question is whether you want to evaluate individual axes. Using Thomas’ example, images 1-5 would be considered and used for the couch 2d iso diameter and 6-9 for the collimator 2d iso diameter.